1. Field of the Invention
The invention relates to a hybrid vehicle that includes an internal combustion engine, having an in-cylinder injection valve and a port injection valve, and an electric motor as drive sources (power sources), and that travels while controlling an output torque of each of the drive sources. The invention also relates to a method for controlling the hybrid vehicle.
2. Description of Related Art
A hybrid vehicle includes an internal combustion engine and an electric motor as drive sources that generate driving force for propelling the vehicle. That is, the hybrid vehicle travels by transmitting torque, which is generated by at least one of the engine and the electric motor, to a drive shaft connected to drive wheels of the vehicle.
Incidentally, a hybrid vehicle may also include an internal combustion engine that includes a fuel injection valve that directly injects fuel into a combustion chamber (that is, in-cylinder injection valve) and a fuel injection valve that injects fuel into an intake port that communicates with the combustion chamber (that is, port injection valve). One of such hybrid vehicles that include an engine having an in-cylinder injection valve and a port injection valve is configured to execute any one of a port injection drive mode, an in-cylinder injection drive mode and a common injection drive mode for the purpose of carrying out various abnormality diagnoses (for example, see Japanese Patent Application Publication No. 2005-226553 (JP 2005-226553 A)). The port injection drive mode is a mode in which the entire amount of fuel that is supplied to the engine is injected from the port injection valve. The in-cylinder injection drive mode is a mode in which the entire amount of fuel that is supplied to the engine is injected from the in-cylinder injection valve. The common injection drive mode is a mode in which fuel is injected from both the in-cylinder injection valve and the port injection valve.
Incidentally, the hybrid vehicle determines an engine required power on the basis of a torque that is determined on the basis of a user's accelerator operation amount (that is, a user required torque that is required to rotate the drive shaft of the vehicle). Furthermore, the hybrid vehicle controls the engine at an engine operation point in a first engine operation line (optimal engine operation line) such that the power of the engine satisfies the engine required power and the operation efficiency of the engine is optimal.
On the other hand, in the above-described engine, when it is determined that a misfire has occurred in the case where the engine is being operated in the common injection drive mode, it is desirable to be able to identify whether the misfire has occurred due to an abnormality of the in-cylinder injection valve or the misfire has occurred due to an abnormality of the port injection valve. In order to identify which injection valve causes a misfire, it is required to operate the engine in one of the in-cylinder injection drive mode and the port injection drive mode.
On the other hand, when the port injection drive mode is continued in a state where the load of the engine is relatively high, the temperature near a fuel injection hole (nozzle) of the in-cylinder injection valve becomes excessively high. Thus, it is difficult to make the above identification by continuing the port injection drive mode in a state where the load of the engine is high. In contrast to this, in a state where the load of the engine is relatively low, it is possible to continue the port injection drive mode and the in-cylinder injection drive mode over a relatively long period of time although there is a limit.
Thus, when it is determined that a misfire has occurred in the case where the engine is being operated in the common injection drive mode, it is conceivable to identify (determine) which injection valve is abnormal by decreasing the load of the engine and operating the engine in one of the in-cylinder injection drive mode and the port injection drive mode and, in this case, determining whether a misfire occurs.
However, when the operating state of the engine is simply changed from a high load state to a low load state, an engine output torque decreases, so a torque that acts on the drive shaft becomes smaller than the user required torque and, as a result, the user may experience a feeling of strangeness. Furthermore, depending on the characteristics of the in-cylinder injection valve and port injection valve, it may be possible to operate the engine in one of the in-cylinder injection drive mode and the port injection drive mode in a predetermined load range other than a low load range. In this case, in order to identify which injection valve is abnormal, it is conceivable that the operating state of the engine is changed from a low load state to a high load state. At this time, the engine output torque increases, so the torque that acts on the drive shaft becomes larger than the user required torque, so, still, the user may experience a feeling of strangeness.